Catalogue of Organisms will be going through something of a hiatus for the next month or so (just in case anyone would have noticed) as yours truly will be 'going home', as I might have said if I'd been living in 1890. Two weeks in England, followed by a week in Jordan, which, in the way of holidays, seems to add up to four weeks away. After that, barring accidents, it should be business as usual.
The extinction event at the end of the Cretaceous is often seen as something of a changing of the guard: the old Mesozoic fauna was swept away, leaving the world open for the (eventual) rise of our modern Caenozoic fauna. However, not every lineage that crossed the Cretaceous boundary remains with us today.
Skull of Kamptobaatar kuczynskii in lateral view, without lower jaw. From Kielan-Jaworowska (1971).
Multituberculates (multis to their friends) were a group of small, vaguely rat-like mammaliaforms that first appeared in the Middle Jurassic (but see comments later). The name 'Multituberculata' refers to their most distinctive character: the presence of a particularly large number of tubercles (cusps) on the post-canine teeth, in particular on the fourth premolars and first molars of the upper jaw. The first upper molars of Kamptobaatar kuczynskii, for instance, had ten cusps, arranged in two rows of five (Kielan-Jaworowska 1971). These multi-cusped teeth were faced on the lower jaw by a massively enlarged fourth premolar, which had become high and multi-ridged, like some sort of dental buzz-saw. These massive teeth, together with the loss of the canines in all but a few basal species (Kielan-Jaworowska & Hurum 2001), have been interpreted by most authors as indicating a diet of tough plant matter, like that of most modern rodents, though some small animals such as insects may have also been eaten. As such, multis are commonly regarded as the first mammaliaforms to show obvious adaptations for a vegetarian diet.
Lower jaw of Kamptobaatar kuczynskii, showing reduced dentition between incisor and enlarged fourth premolar. From Kielan-Jaworowska (1971).
For the most part, multituberculates are known from Eurasia and North America, though Hahnodon taqueti is known from the Lower Cretaceous of Morocco, and potential multituberculate teeth have been identified from the Late Cretaceous of South America (Kielan-Jaworowska & Hurum 2001). The Late Cretaceous Gondwanatheria may also represent South American relatives of the multituberculates (Gurovich & Beck 2009). A number of lineages of multis passed through the end of the Cretaceous apparently unscathed, and multituberculates remained a part of the Holarctic fauna up until the end of the Eocene. Their final extinction is usually attributed to competition from the increasingly diverse placentals, particularly the rodents (Kielan-Jaworowska et al. 2004). This may have been related to their reproductive biology: multituberculates had extremely narrow and rigid pelvic girdles that could not have spread much during birth, and they must have produced extremely small young in a similar manner to modern marsupials (Kielan-Jaworowska et al. 2004).
Reconstruction of the North American Palaeocene multituberculate Ptilodus, from Cox (1998) via here.
Some of you may have noticed that I have referred to multituberculates as 'mammaliaforms' rather than 'mammals': they were definitely the former, but it is more debatable whether they are the latter. Most modern authors restrict the name Mammalia to the mammal crown-group: that is, the smallest possible group including monotremes, marsupials and placentals. The question of where multis sit in relation to the mammalian crown-group requires me to mention another group of animals, the Haramiyida, that lived in the Late Triassic and early Jurassic. Haramiyidans have teeth similar to the distinctive arrangement of multituberculates, leading to the assumption when they were first described that they represented early multis (Kielan-Jaworowska & Hurum 2001). However, while multituberculates share a number of features of the non-dental skeleton (such as ear ossicles independent of the jaw) with modern mammals, haramiyidans have an overall anatomy of a much more plesiomorphic grade. If multituberculates are related to haramiyidans, as indicated by their teeth, they would be well outside the mammalian crown group, and would have evolved a number of convergent features independently of mammals. On the other hand, if one goes by the evidence of features other than the teeth, multis were closely related to mammals (either their sister group [Gurovich & Beck 2009] or within the mammal crown, closer to marsupials and placentals than to monotremes [Luo et al. 2002]) and haramiyidans represented an entirely independent acquisition of a multituberculate-like dentition. At present, an independent origin of multis and haramiyidans seems more likely, but it could easily be upset by future discoveries.
Gurovich, Y., & R. Beck. 2009. The phylogenetic affinities of the enigmatic mammalian clade Gondwanatheria. Journal of Mammalian Evolution 16: 25-49.
Kielan-Jaworowska, Z. 1971. Skull structure and affinities of the Multituberculata. Acta Palaeontologica Polonica 25; 1-41, pls 1-5.
The latter part of the Ordovician saw a turnover in the graptoloids, the planktonic branch of the early Palaeozoic colonial graptolites (earlier posts on graptolites can be found here and here). The basally-branched forms that had been among the earliest graptoloids became extinct, leaving only the scandent forms surviving in the Silurian. Scandent colonies grew as a single linear stipe, which might have thecae (the openings for individual members of the colony) in two lines, one on either side of the stipe, or in a single line on one side of the stipe. The latter form characterised the Monograptidae, which were to become the latest surviving graptoloids (Bulman 1970).
Despite their long survival, monograptids were mostly a fairly uniform bunch. Their simple morphology did not give much scope for obvious morphological variation, and many monograptid lineages were not greatly distinct in colony form. One of the more distinct forms was the short-lived genus Rastrites which occurred during the Llandovery period of the early Silurian (and so relatively early in the history of the monograptids). Species of Rastrites developed very long and slender, widely spaced thecae that stode out perpendicular from the connecting stipe like the strings on an Incan quipu.
Rickards et al. (1977) suggested that the genus Rastrites is polyphyletic, deriving separate lineages within the genus from a number of different (albeit closely related) species assigned to the separate genus Monograptus. To a certain extent, the distinction is a little arbitrary: these ancestral Monograptus (treated by some authors as a third genus, 'Demirastrites') also had elongate thecae, but not yet to the same degree as developed by Rastrites proper, and not as widely spaced. But that, after all, is the nature of evolution, and the limitation of any classificatory system. You have to draw a line somewhere.
Bulman, O. M. B. 1970. Graptolithina with sections of Enteropneusta and Pterobranchia. In Treatise on Invertebrate Paleontology Part V 2nd ed. (C. Teichert, ed.) pp. V1-V149. The Geological Society of America, Inc.: Boulder (Colorado), and the University of Kansas: Lawrence (Kansas).
While flicking through my reference cabinet the other day, I came across something interesting from a few years ago:
Knowles, B., K. Rowlands et al. 2006. Promotion of entomological research through popular music. Science Outreach 1: 5-26.
Most of you will probably be familiar with Beyoncé Knowles and Kelly Rowlands, whose performances in the singing group Destiny's Child have led both not only to chart-topping musical success, but also to acting careers that deserve to be ranked with such luminaries as Susan Cabot and Barbara Payton. What does not seem to garner anywhere near as much attention is that both are also keen amateur researchers. In 2006, they released a pop single commenting on the demands of their research, together with the above article in which they discussed their intent in doing so. Unfortunately, the criminal inattention by the world of popular music to entomology meant that Knowles' and Rowlands' real intent went largely unremarked.
Knowles presenting a paper on size distribution of termite mounds.
Contrary to popular belief, when Knowles stated in the hit song in question that she needed a 'soldier', she was not expressing a desire to date a forthright individual who provide her with the comforts of life. Rather, she was discussing requirements for her preferred interest, the taxonomy of subterranean termites. As anyone who has worked on these animals could tell you, it is exceedingly difficult if not impossible to distinguish termite workers to species level; a complete ID requires individuals of the more specialised castes. Knowles has mentioned that, as well as its own inherent fascination, she finds her termite work a great help in maintaining her figure. Digging up ground in search of termite colonies can be hard work, especially when doing so in pumps.
Rowlands demonstrating one of her most vital pieces of lab equipment.
Rowlands, on the other hand, finds more to interest her in the lab. She never meant to reject those whose 'status ain't hood' but those that weren't hud: the gene product (hypo-uric dehydrogenase) whose effects she studies in Sophophora melanogaster*. Flies expressing higher than normal levels of hud have shown a distinct (and so far unexplained) tendency to cover themselves in flakes of mica and create a staccato drumming with their forelimbs.
*When asked for her comment on the recent ICZN application regarding this species, Rowlands sniped, "I don't think they're ready for this name-change".
Despite the lack of recognition given to their investigations, both performers remain devoted to biological research. Knowles has since moved into fashion, and has referred to a desire to model a line on the patterning of buprestid beetles: 'Cover Yourself in Jewels'.